If your browser does not support row-gap, the content will be darkgreen with a dashed border.
.box { border: 4px solid blue; color: blue; } @supports not (row-gap: 10px) { .box { border: 4px dashed darkgreen; color: darkgreen; } }
<div class="box"> If your browser does not support row-gap, the content will be darkgreen with a dashed border. </div>